1. Field of the Invention
The present invention generally relates to IC cards and particularly relates to IC cards having a fault checking function.
2. Description of the Prior Art
Generally, an IC card has a structure as shown in FIG. 1. That is, an IC card 1 has a card core 2 made of, for example, a plastic material and formed with a recess 3 in which an IC module 4 is accommodated. One or two LSI chips are mounted on the IC module 4. The IC module 4 is provided with eight contact terminals 5 through which an electric circuit including the IC module 4 and an external circuit are electrically connected with each other.
The recess 3 is filled with a filler 6 to protect the IC module 4. Printing layers 7 and 7' are bonded on the opposite surfaces of the card core 2. Designs, characters, marks, or the like, are printed on the printing layers 7 and 7' if necessary, and the surfaces of the printing layers 7 and 7' are coated with surface layers 8 and 8' for protecting the printing layers 7 and 7' respectively. Although FIG. 1 is illustrated with exaggeration particularly in thickness, the actual thicknesses of the card core 2, each of the printing layers 7 and 7', and each of the surface layers 8 and 8' are finished to be, for example, 0.55 mm, 0.1 mm, and 0.02 mm, respectively, so that the total thickness of the card is about 0.8 mm.
FIG. 2 is a block diagram showing a structure of an IC included in the IC module 4. The IC includes two chips, that is a CPU chip 40 and a memory chip 41. The CPU chip 40 includes a CPU 401 which perform control in accordance with a program, a ROM 402 which stores the program and so on, and a RAM 403 which temporarily stores data in the midway of a process executing the program. The memory chip 41 has a PROM 411 in which various data are mainly stored. Of various kinds of PROMs, used is an EPROM which is a PROM erasable by ultraviolet rays (when embedded in an IC card, the data stored therein cannot be erased unless a window is formed for allowing ultraviolet rays to pass therethrough), or an EEPROM which is an electrically erasable PROM (that is, data stored therein can be electrically erased).
Since an IC card is made very thin in its thickness, there often occurs a fault in an electric circuit in the IC card, for example, disconnection, shortcircuit, etc., due to mechanical stress, particularly bending, shocks, or the like, and sometimes a fault may be generated in the process of manufacturing the IC card. A fault often generated in an IC card is disconnection caused mainly at four portions shown by four arrows in FIG. 1. Another fault is damage or the like of a memory due to static electricity. If there occurs such a fault, it becomes impossible to carry out data writing/reading operations, or the data writing/reading operations become erroneous. If address lines are partly disconnected, a writing area may be erroneously selected or erroneous data may be read out, and if data lines are partly disconnected, data to be written/read may be changed. Particularly, if disconnection is caused in control lines or in a power supply line, the IC card becomes unable to be used.
In the conventional fault check of an IC card, for example, such a method has been employed in which general data are recorded in a memory in advance and an operator reads the data out of the memory so as to judge whether the data processing can be correctly performed or not on the basis of the read-out data.
In such a method, however, there are problems as follows. Upon occurrence of such a fault that any one of data or address lines is disconnected or touches another line, it may happen that the fault does not influence an address or data to be used for the fault check. In such a case, it may be concluded that the IC card is normal in spite of existence of a fault, thereby lowering reliability of the fault check.
Generally, an IC card is vulnerable to mechanical shocks, bending, and static electricity. An IC card is usually carried by a user and effected by various external conditions. Not only mechanical shocks may break an IC card, but an atmospheric discharge of static electricity may damage an IC memory per se, and particularly, there may occur a fault due to a discharge caused when clothes of chemical fibers of the IC card possessor touch a metal piece. On the other hand, IC cards are often used for the management of incoming/outgoing of money, for the management of health, etc., and therefore correctness is required particularly for the data writing/reading operations and erroneous operations should be prevented.